Recently, advanced safety services providing information/giving warning/performing intervention control for vehicles based on position information of mobile objects such as vehicles to reduce traffic accidents, have gained attention. Specifically, for example, an advanced safety service is a service that prevents traffic accidents due to blind spots, carelessness, and oversight on the part of a driver by providing position information concerning the vehicle operated by the driver as well as other vehicles, signal information, and sign information to a vehicle entering a predetermined range from an intersection, a bend, etc., (e.g., within 100 m from a center portion).
With such advanced safety services, highly accurate position location is required with respect to the vehicle position of the driver, which is provided to other vehicles and compared with the positions of other vehicles, signals (or stop line), and signs. Specifically, for example, if the position of another vehicle provided by the advanced safety service is different from the position of the vehicle visually recognized by the driver, the driver feels confused or uncomfortable and therefore, a position locating error with respect to each of the vehicles is desirably within a half-length of a vehicle (e.g., about 2.5 m).
Currently, vehicle position locating technologies include Global Positioning Systems (GPS) utilized for car navigation systems. However, if a vehicle is surrounded by trucks and buses having higher vehicle heights or if the vehicle travels in an urban area with high-rise buildings randomly located, position location through GPS may become inaccurate due to poor tracking of GPS satellites, the occurrence of multipaths, etc.
On the other hand, autonomous navigation in which the distance traveled by a vehicle is measured by vehicle speed pulses, an acceleration sensor, a gyroscope, etc., is known to have fewer errors in the case of traveling within a predetermined range. Specifically, for example, an error of a travel distance for autonomous navigation is 2.0 m or less for travel within an advanced safety service area (e.g., about 100 m) where the above advanced safety service is provided. Therefore, if accurate position location is performed upon entry to the advanced safety service area, highly accurate position location (e.g., within an error of 2.5 m) is enabled in the advanced safety service area via the autonomous navigation.
Technologies of accurate position location at the position of entry into an advanced safety service area include Ultra Wide Band (UWB), magnetic markers, and ultrasonic positioning.
The position location at the position of entry into the advanced safety service area is also performed through the utilization of optical beacons, which are existing infrastructure facilities, instead of UWB, magnetic markers, ultrasonic positioning, etc. Position location utilizing optical beacons is a technique of correcting a vehicle positioning result of GPS with the use of position information of an optical beacon included in an optical signal emitted by the optical beacon, for example.
For the reception of an optical signal emitted from an optical beacon, it has been proposed to provide a cover on a receiving unit of an on-vehicle device to block optical signals from outside the communication area of the optical beacon passed by a vehicle (see e.g., Japanese Laid-Open Patent Publication No. H11-296793).
It has been proposed to detect passage of a vehicle through a boundary of a communication area where an on-vehicle device communicates with an optical beacon, to correct the boundary position to the vehicle's current position at the time of the detection (see e.g., Japanese Laid-Open Patent Publication No. 2003-107143).
A conventional method of position location using an optical beacon will be described with reference to FIG. 19. FIG. 19 is an explanatory diagram of a position locating system using an optical beacon. As depicted in FIG. 19, a position locating system 1900 is made up of an optical beacon 1901 and an on-vehicle device 1903 equipped on a vehicle 1902.
The optical beacon 1901 is disposed on a roadside and through the on-vehicle device 1903, transmits and receives various signals 1910 with respect to the vehicle 1902 traveling in a communication area 1920. Specifically, for example, the various signals 1910 transmitted/received include downlink (DL) signals transmitted from the optical beacon 1901 to the on-vehicle device 1903 and uplink signals transmitted from the on-vehicle device 1903 to the optical beacon 1901.
More specifically, for example, the DL signals are optical signals that include road traffic information distributed from a Vehicle Information and Communication System (VICS, registered trademark) center, position information related to the position of the optical beacon 1901, ID (identifier) information of the optical beacon 1901, etc.
The on-vehicle device 1903, using an optical receiving apparatus not depicted, receives optical signals emitted from the optical beacon 1901 to locate the current position of the vehicle 1902 through GPS, autonomous navigation, etc. Specifically, for example, the on-vehicle device 1903 is configured to locate the current position by correcting a positioning result of the vehicle 1902 using position information related to the position of the optical beacon 1901 acquired from the optical signal received by the optical receiving apparatus.
The communication area 1920 is an area where the optical beacon 1901 and the on-vehicle device 1903 may communicate and is a range of a distance L along the traveling direction of the vehicle 1902 and a width W along the vehicle width direction, for example. The on-vehicle device 1903 is configured to locate the current position of the vehicle 1902 using the optical signal received at a position within the range of the communication area 1920.
However, if UWB, magnetic markers, ultrasonic positioning, etc., are utilized to accurately perform the position location in the above conventional technologies, a new device must be equipped on the vehicle, imposing burden and cost to the driver.
On the other hand, if the position location is performed with the use of the optical beacons, which are increasingly deployed as infrastructure facilities, to constrain the burden and cost to the driver, errors may occur depending on the range of a communication area of an optical beacon. An error may occur because the position of reception of the optical signal is different from the position of the optical beacon.
Specifically, for example, since a predefined communication area of an optical beacon extends about three to four meters in the vehicle traveling direction and the vehicle width direction, an error in the vehicle position location may be as much as three to four meters. Even if optical signals from outside the communication area such as from the opposite traffic lane are blocked in Japanese Laid-Open Patent Publication No. H11-296793, an error occurs in the vehicle position location depending on the range of the communication area of the optical beacon emitting the optical signal that is received.
Japanese Patent Application Laid-Open Publication No. 2003-107143 recites that a boundary position predefined for an optical beacon is corrected to a current position of a vehicle at the time of detection of the boundary of the communication area through the reception of an optical signal. However, the range of the communication area of the optical signal varies because of weather conditions such as rain and fog, dirt on optical signal transmitting/receiving units, reduced reception sensitivity due to blocking by wipers, etc., and contrarily, may be as much as 12 m.
Therefore, if an error occurs between the detected boundary position and the predefined boundary position, error in the vehicle position location increases. Even at a position that is not the predefined boundary position, an error occurs between the detected boundary position and the predefined boundary position by receiving the optical signal from the optical beacon.
If an error occurs in the vehicle position location and the appropriate position location of the current position is unfeasible, the driver misperceives the positional relationship between the vehicle of the driver and a feature such as a traffic signal and an intersection, causing unnecessary confusion and an uncomfortable feeling.
Particularly, with the advanced safety service, when safe travel by vehicles is promoted through the utilization of relative positions of the vehicle of the driver and another vehicle, the driver is put at risk by an error in the position location of the current position of the other vehicle provided from the other vehicle.